The invention relates to a switch for combined heater plug or ignition and starting circuits and for independent switching of a plurality of load circuits, the switch being of the type which includes at least two spring biased contact arms arranged in a rotary driver or switching wheel, the arms being insulated one from the other and each cooperating at one end thereof with annular cams; the cams lift and lower during the rotation of the arms contact studs attached to the arms opposite a counter-contact ring which is fixed around the axis of rotation of the arms on a socket of the switch; a plurality of load contacts are mounted in the socket around the counter-contact and cooperate with the other end portions of the arms.
A known switch of this type for controlling the ignition circuit in a motor vehicle is known from the German published patent application No. 2,555,110 and includes a socket having a central contact and a plurality of load contact terminals arranged about the central contact. The driver or switching disk of the switch supports a bridging element which is permanently connected to the central contact via a contacting stud of a double contact member which is aligned with axis of the switch and biased by a spring. The double contact member has a finger which sweeps across the load contacts. In addition, the driver or switching disk supports a switching bridge having a contact arm abutting against a shaped contact member. The shaped contact member can be raised and lowered into engagement with another contact stud of the double contact member and has a contact arm which also sweeps across the individual load contact terminals.
Similar switches for the ignition circuits of motor vehicles are described in the German utility model applications Nos. 6,801,832 and 7,310,447 and are also based on the aforedescribed conventional designs utilizing a single liftable switching bridge. Provided that such known designs are intended for switching additional circuits, it would be necessary to provide a further liftable switching bridge on the driver or switching wheel and this double switching bridge arrangement would haved to be coupled via a connecting piece to the central contact and to one of the contact studs of the double contact member and to act with its switching arm on an additional profiled contact piece, whereby the contact surface of this additional switching bridge would have to cooperate as a lifting contact with the counter-contact on the socket of the switch.
In the known switches of this type all current is fed to the central contact and all contact members of respective load circuits are of necessity directed to this center contact arranged in the axis of rotation of the switch.
Such a prior art design of switches having several superposed central contacts arranged along the rotary axis however, has the disadvantage that each of the employed contact studs must be designed for a relatively long switching trip in order to avoid a premature or a completely unintended contact and to ensure a proper switching action. Difficulties arise however when an excessive clearance between the respective switching studs takes place inasmuch as the control of contact arms supporting the contact studs is effect by means of cam disks concentrically arranged on the housing of the switch around its rotary axis. The limited space within the housing permits, however, only a limited pitch of such cam plates between the individual stop points of the switch and consequently the pitch of the cams and thus the lift or trip of the controlled contact studs cannot exceed a predetermined value. Moreover, a conventional switch of this type is oversized in axial direction and this is again disadvantageous for the design of stop cams between the driver or switching wheel and the housing of the switch; these stop cams cooperate with spring biased drop-in pins normally arranged on the driver or switching wheel.
Since the cam rings for controlling the axial movement of contact arms are arranged on the periphery of the socket for the switch housing and have, consequently, only a limited length, there arise difficulties when an increased number of load circuits is to be successively switched on by means of contacts arranged side-by-side in small angular increments.